In particular, the invention relates to a formulation that has a specific gravity between about 0.7 and about 1.6 is rich in silica fume or an acceptable substitute and hence contains high proportions of water as well as fly ash, and entrains air and thus provides higher yields compared the conventional cements.
Oil recovery from heavy oil and CBM fields requires sealants or cements that are tolerant to steam, carbon dioxide, and also hydrogen sulfide. Portland cement based formulations do not perform well in such environments. Phosphate cements, being tolerant to steam and other named gases, are more likely to be successful. The formulations disclosed earlier, such as in U.S. Pat. Nos. 6,561,269 and 6,910,537, the entire disclosures of which are incorporated by reference, however, need to be suitably modified to increase the yield and lower the cost, be tolerant to steam injection, so that they can effectively compete with the cements used at present in such fields. This invention includes such formulations.
The sealants or cements for heavy oil and CBM fields must satisfy the following requirements:
1. The cements should be ultralight to match the density of the formation. Heavier cements tend to fracture the formation resulting in water intrusion during setting of the cements.
2. The cements should be tolerant to steam injection and stable in hydrocarbon and sulfide and sulfate environments.
3. The cost of these cements should be low.